x3 No problem~!
It's based on a combination of different folk lore traditions, really - Primarily that of the 'Benandanti'. It was believed in the Fruili province of Italy that people born with the 'caul', with the amniotic sack still partially covering their head (or, more rarely, their entire head and part of their back) had a series of special 'powers' as a result, the power to be able to recognise witches, cure children and people cursed by them and, each year on the 'Ember Days' would go out at night in spirit form to 'fight the witches'.
The 'battles' encompassed, generally, the two sides gathering at a designated place and sparring with each other, the Benandanti with stalks of fennel and the witches with sorghum stalks (the stuff they used to make broom handles out of). They would 'fight' over the fertility of the different harvests: grain, grapes and fruit, etcetera, and if the Benandanti won, it was believed the harvest would be good, and if the witches won the harvest would fail. Details of the gatherings otherwise vary, but in some strands of the belief there were large feasts, attended by animals, spirits and faeries etcetera. If a man or woman kept the caul they'd been born in (their families often did and had masses said over them), when they turned 20 they'd be called to the Benandanti ranks.